Treating hydrocarbon fluids



B. l. SMITH TREATING HYDROCARBON FLUIDS New.l 28, 1944.

"2 sheets-sheet 1 Filed Jan. 2, 1941 Y@ Q m TREATING HYDROCARBON FLUIDSFiled Jan. 2, 1941 2 Sheets-Sheet 2 mmmm| cas fuif GIE)- ogncoo-I-ooo miam cgggogoggggg o8 ooo o o ooo oo y 252 .000@ 23o l vfV 232 PatentedNov. 28, 1944` Brook I; smith, minuta,- N. J., assignmte Standard OilDevelopment Company, a corporation of Delaware Application January 2,1941, Serial No. $12,853 2 Claims. (Cl. 2611-668) This invention relateste the thermal conversion of relatively heavy hydrocarbons to formunsaturated lower boiling hydrocarbons.

According to this invention, relatively heavy hyi j drocarbon oils suchas gas oil or the like are heated to 'a relatively high temperature inthe l presence of steam and under a relatively low introduced into thecollecting drum.

The distillate from the collecting drum is passed pressure to convert arelatively large portion thereof to lower boiling unsaturatedhydrocarbons such as ethylene, propylene, butylene, butadiene,

This invention is primarily conand the like. cerned with the productionof ethylene which may be used las a startingproduct in the manufactureof other chemical compounds. The conversion takes place at a relativelyhigh temperature and during the conversion, gasoline constituents arealso formed which are mostly aromatic in character so that an aromaticgasoline'is also recovered as one of the products. However, thelinvention is so carried out that the largest percentage of ethylene isobtained without serious deposition of coke in the conversion zone.

More specifically, the invention includes heating a relatively heavy oilto a vaporizing temperature and in the presence of steam and thenpassing the heated relatively heavy. oil to a separating zone toseparate unvaporlzed constituents from` The hydrocarbon vaporshydrocarbon vapors. and the steam are passed through a conversion zonewhere the hydrocarbon vapors are heated to alrelatively high temperatureto effect the desired extent of conversion and the production of arelatively large amount of ethylene. I'he products of conversion leavingthe conversion zone are` quenched with a relatively cool cycle gas oiland the quenched mixture is introduced into the lower portion of afractionating tower to separate liquid residue from vapors. Theseparated vapors are fractionated to separate Va cycle gas oil and tarfrom volatile constituents passing overhead from the fractionatingtower.

The overhead vapors are cooled t0 condense normally liquid constituentsand water. The water is withdrawn from a separator as the lower layer.The normally liquid constituents or distillate is withdrawn as the-upper layer. The uncondensed vaporsare passed into a knock-out drum toseparate any liquid constituents theref. am. 'I'he uncondensed vaporsare then passed through a first stage compressor to raise the pressureon the vapors and the compressed vapors are cooled under pressure, andwith the distillate introduced into an intermediate knock-out drum forseparating condensed constituents such as water as the lower layer. Inthis drum uncondensed vapors are separated from distillate andcompressed in a second stage compressor and again cooled before beingintroducedinto a collecting drum. 'I'he distillate is withdrawn from theintermediate knock-out drum as an upper layer, also has its pressureincreased and is to a fractionating tower where volatile constituentsare removed from normally liquid hydrocarbons which are withdrawn fromthe bottom of the-tower as an aromatic fraction suitable for use inmotor fuels.

The vapors passing overhead from the last mentioned fractionating towerare mixed with uncondensed vapors from the collecting drum abovedescribed and the combined vapors are then treated in any suitablemanner as by a series of fractionating towers to separate a lightfraction containing methane and ethylene,- another fraction comprisingmostly ethylene, another fraction containing mostly propylene, anotherfraction containing butylenes and butadiene and a nal fractioncontaining light aromatieconstituents suitable for use in motor fuels.The ilrst fraction containing methane and ethylene may be used as suchwithout the removal of methane in a chemical process for reacting theethylene with any desired reagent. For example, this fraction may beusedl in the manufacture of ethyl chloride without removing the methanefrom the mixture. fThe light aromatic constituents are preferablycombined with the separated aromatic distillate above described. The C4fraction is preferably treated in any suitable manner to separatebutadiene from the butylenes.

As above stated, any suitable fractionation system may be used forseparating the desired fractions from the vapors and gases. Afractionation process especially adapted for separating these fractionsis` disclosed and claimed in a separate copending application illed forSmith et al., the

application bearing Serial No. 372,854 and having .Figure 1 represents atic showing ofA i apparatus adapted to carry out the process of" ispassed by means of pump l2. The relatively` then heavy oil is preheatedby passing through a heat exchanger I4 where it indirectly contacts hotcycle gas oil separated later in the process as will be hereinafterdescribed. If desired, the preheated feed oil may be passed to anaccumulator.

The preheated relatively heavy oil is passed through line I8 and througha heating coil I8 in the furnace 22 to vaporze a large portion of therelatively heavy hydrocarbon oil under tempertaure conditions at whichsubstantially no cracking occurs. Superheated steam passing through line24 is injected into the latter passes of the heating coil I8.

The heating of the -water to provide the superheated steam will now bedescribed. Water passing through line 26 is forced by means of pump 28through a heat exchanger 32 where it indirectly contacts hot cycle gasoil for preheating the water. The preheated water is then passed througha heat exchanger or heating means 34 where it is vaporized by indirectlycontacting a hot circulating oil. The steam is then passed through aheating coil 36 shown in the drawings as being in a furnace 31 where thesteam is superheated and the superheated steam or a portion thereof ispassed through line 24 into the vaporizing coil I8 as above described.The heating coil 36 is preferably located in the conversion furnacelater to be described.

The vaporizing furnace 22 is shown diagrammatically in Figure 1 in orderto simplify the showing in the drawings. In Figure 2 there is shown thestructure for a vaporizing furnace which is preferably used forvaporizing the heavy oil. The construction or apparatus shown in Figure2 will be more specifically described hereinafter.

duced into the upper portion of the fractionating tower 42 as reux toassist in removing higher boiling hydrocarbons from the vapors. Thecycle oil is introduced into the'tower 42 through une 41.

The furnace or heater 54 is diagrammatically shown in the drawings inorder to simplify the drawings and to facilitate understanding of theinvention. A furnace orheater especially adapted for heating hydrocarbonvapors to conversion temperatures,y for superheating the steam, forheating the circulating oil stream, for preheating the oil vapors to becracked and for soaking thev hydrocarbon oil vapors at conversiontemvided at the top of the radiant heating sections The heatedrelatively heavy hydrocarbon oil and steam leave the vaporizing coil I8through line 38 and are introduced into the lower portion low heat inputor drying zone immediately on entering the' cracking furnace such as thecons vection section to allow time for coking of liquid particles whichmay be carried over from the first separatingzone. The convectionpreheating section in furnace 54 may be referred to as thev vapor feeddrying zone. The dried vapors are then passed through the radiant andsoaker sections comprising the conversion zone. The

conversion coil is diagrammatically shown on the drawings.

During passage through the conversion coil 55, the hydrocarbon vaporsare rapidly heated to a relatively high temperature and are maintainedin the coil for a suiiicient period of time to effect the desired extentof conversion and the production of an appreciable amount of unsaturatedlower boiling hydrocarbons such as ethylene and butadiene.

During fractionation of the vapors in the fractonating tower 42, cyclegas oil recovered 'from 'a later stage in the. process is preferablyintroand at the ends ofthe radiant heating sections and combustion gasesare withdrawn from the bottom of the radiant heating section andintroduced to the common convection section. Oill vapors and steam fromthe fractionator 42 are passed through a cooler part of the convectionheating section in four separate streams to preheat and dry the vaporsas above described. The separate streams are then each passed through asingle row of wall tubes in the radiant heating sections to heat thestreams to conversion temperature. Each radiant section has two rows ofwall tubes and the separate streams are separately heated in the radiantsections.

The separate streams of oil vapors as they leave the radiant sectionsare at conversion temperature and each stream is separately passedthrough a soaking section in which the oil vapors are maintained atconversion temperature for the required period of time. The soakingsection may be in one section but it is preferably divided into twoportions and each portion is located in the hottest portion of theconvection section. In the specific construction the soaking section isdivided into two portions corresponding tothe two radiant sections andthe soaking tubes are arranged in the upper part lof the passagewayforming part of the convection sect-ion, the remaining unobstructedlower partof the passageway being provided with a damper for controllingthe heating ofthe soaking tubes. From the soaking tubes, the separatestreams are combined and passed through transfer line 56 :as .shown inthe drawings. Preferably the stream from each soaker section is -passedas a separate `stream to the tower 62.

lFor preventing voverheating cof the loil vapors A in the soakingsections,l Vthe steam .superheater shown at 59 in the vdrawings isLarranged in the hottest portions of the convection section `ahead ofthe soaking tubes or sections :in the vfurnace 54. Arranged in thecoolest part fof the convection section of the furnace 54 and vabove thepreheating section above described is arranged the coil for heating theoil stream "which is circulated through vheat exchanger 34 and forproviding heat in other steps in the xpiocess `as will vbe i hereinafterdescribed.

From the above, it will be seen `thatthe heating of a vplurality rofstreams is brought about in a single furnace and in this way `better andmore eiecient Vheating is effected.

be described hereinafter.

aseaaos The products of conversion leave the conversion coil 55 at anelevated temperature and in order to prevent undue cracking, quench oilis introduced into the products of conversion by' means of line 58 toVreduce the temperature of the products of conversion. Coke 'depositionin the transfer line 66 and second separating zone 6l is avoided byquenching the reaction products to a temperature above the point atwhich condensation of the reaction productswill occur. The quench oilcomprises a portion of thecooled cycle sas oil above referred to whichis recovered in the later steps of thisprocess and will 'I'he quenchedproducts of conversion are introduced into the lower portionl orseparating reuxina medium to assist in the fractionation of the vaporsin the tower 82.

Steam is `directly introduced into the bottom portion of fractionatingtower 42 and if necessary may be introduced into the bottom portion oftower 62 to assist in removing volatile constituents from the heavyhydrocarbons accumulating in the bottom .portions of thesefractionators.-

Steam .for this purpose is taken from the stream of superheated steamleaving the superheating coil 88 above described. A portion of thesuperstituents. The sensible and latent heat remainheavier constituentsfrom the vapors, redux oil is introduced into lthe lower portion 60 ofthe fractionating tower 62 by means of line 68 below the trap-out tray12. The reflux oil is preferably a portion of the cooled cycle gas oilwhich is used as quench in line 58 above described. Y e Relatively heavyhydrocarbons collect on the trap-out tray 'I2 from which they are drawnby means of line 'I4 and introduced4 into an accumulator 16. Therelatively heavy hydrocarbons withdrawn from trap-out tray 'l2 formthe'cycle oil which has been above referred to. The cycle oil collectingin the accumulator I6 is withdrawn therefrom and passed throughline I8by means of pump 82 and a portion thereof is introduced into the upperportion of the fractionating tower 42 by means'of line 41 as abovedescribed. 'Another portion of the cycle oil is passed through line `84by means of a pump 86, if necessary. the

hot cycle oil passing through line 84 being passed through heatexchanger 92 for preheating the water to be used in the process 'andthen through heat excahnger |4 for preheating the relatively heavyhydrocarbon feed oil passing through line l0. In passing through theseheat exchangers the cycle oil is cooled. The cycle oil is thenpreferably further cooled by passing through a water cooler 88 or thelike and a portion of the cooled oil may be passed to an accumulator 90.The cycle gas oil is withdrawn from accumulator 90 through line 9| andmay be withdrawn from the process through vaived line 92 or it may bepassed v through line 9| by pump 99 and recycled to and mixed with thefresh feed passing through line |0.

Preferably, a portion of the cooled `cycle oil is passedthrough line 94and used as quench oil and reduxing medium. A portion of the cooledcycle oil is passed through line I8 as quench and throughsline i8 asreiluxing medium as above'described. Another portion ofthe cooled cycleoil is preferably through line 96 and introduced into the intermediateportion of the fractionating tower 62 above the trap-out tray 12 asheated steam and preferably about 50% ofthe steam passing through line24 is withdrawn therefrom, passed through lines 98 and |02 and directlyintroduced into the bottom portion of the fractionating tower 42.Another portion of the superheated steam passingV through line 98 may bepassed through line |04 and directly 'introduced into the bottom portion60 of the fractionating tower 62, but preferably `a separate source ofsteam is used for the bottom of fracfrom through line ||4 and introducedinto the upper' portion of the fractionating tower 62 by means of pump 6as reflux liquid. The drum ||2 is provided with awater draw-off pot H8from which condensed water is withdrawn from the system through line |20and preferably discarded. Uncondensed vapors are withdrawn or passoverhead through line |22.' A portion of the condensed hydrocarbons arewithdrawn through line |24 to prevent building up the liquid level indrum I2. i

The uncondensed vapors are introduced into a knock-out drum |26 forremoving any liquid constituents which may have come over with thevapors and which are withdrawn from the bottom of the drum throughvaived line |23 to the intake of pump |29. The Uncondensed vapors leavethe top of the drum |26 through line |30 and are passed through acompressor |32 for compressing the vapors in a rst stage compression.The vapors under pressure are passed through cooler |36 and introducedthrough line |38 into an intermediate knock-out drum |42. Likewise theliquid hydrocarbons which are withdrawn from drums ||2 and |26 throughlines |24 and |28 are combined and placed under pressure by pump |29 andintroduced into` drum |42. The cooler |36 cools the compressed vaporsand condenses some of the heavier hydrocarbons and water. In` thisknock-out drum any condensed water collects on the bottom of the drumand may be Withdrawn through vaived line |44 and discarded.

'I'he uncondensed vapors pass overhead from the drum |42 through line|46, are compressed to a higherpressure in a second stage compression bypassing through the second compressor |48. The further compressed vaporsare then passed througha cooler |50 and introduced into an accumulatingdrum |54. The cooler |50 causes condensation of additional heavierhydrocarbons and additional amounts of water. The liquid hydrocarbonsare withdrawn from the drum |42 and passed through line |55 by means ofpump |56 which also acts to increase the pressure on the liquidhydrocarbons. The liquid hydrocarbons under increased pressure areintroduced into the accumulating drum |54. Any condensed lighthydrocarbons which are separated from the vapors during cooling andbefore fractionation thereof may be introduced into line `I |55y bymeans of line |58.

Any ccondensed water collecting in the bottom of the drum |54 may bewithdrawn therefrom through valved line E 2. The uncondensed vapors passoverhead through line |64. y

The liquid hydrocarbons are withdrawn from the accumulating. drum |54and are passed through line |68 by pump |68. The liquid hydrocarbons arethen passed through a heat exchanger |12 where they are preheated andthey are then introduced into an intermediate portion of anotherfractionating tower |14. The fractionating tower |14 is provided with aheating coil |16 in the bottom portion thereof. The heating coil |16 isheated by a circulating oil stream which forms a portion of thecirculating oil stream passing through heat exchanger 34 abovedescribed, the circulating oil stream being heated in the cooler portionof the common convection heating section of the conversion furnace 54 asabove described.

In the fractionating tower |14 relatively light constituents such as Cs.C4 and some C5 hydrocarbons are removed from a normally liquid fractionwhich is withdrawn from the bottomof the fractionating tower |14 throughline |18 by means of pump |s2 and is then 4passed through the heatexchanger |12 where the withdrawn hot liquid fraction is used to preheatthe feed to the fractionating tower |14. The partially cooled withdrawnnormally liquid fraction is passed through line |84 to a water cooler|85 and is then passed to storage or withdrawn from the system. Thisfraction withdrawn from the bottom of the tower |14 comprises anaromatic fraction which is suitable for use as a motor fuel or in motorfuels.

The vapors and gases leaving the top of the fractionating tower |14 arepassed through line |86 and condenser |90 for cooling and condensing thevapors and gases.I The cooled vapors and gases are introduced into aseparator |92 for separating liquids from vapors and gases, the liquidsbeing withdrawn from the bottom thereof through line |94 and introducedinto the upper portion of the fractionating tower |14 as reflux liquidby means of pump |96. The uncondensed vapors pass overhead through line|98 and are combined with the vapors and gases passing through line |64as above described and are washed with caustic soda solution orotherwise treated toremove sulfur compounds. The mixture is thenpreferably passed through a drying tower to remove moisture prior tosubsequent low temperature fractionation operations and nally compressedin a third stage compression by passing through the third compressor 200and cooled in cooler 20| .This compressed and cooled mixture of vaporsand gases is introduced into a fractionating system or the like 202.This fractionating system 202 represents a diagrammatic showing of ameans for separating desired constituentsfrom the gaseous mixture. Asabove pointed out, a suitable system for separating these constituentsis set forth in ccpending application Serial No. 372,854 above furtheridentified and the description here given will briefly set forth theproducts resulting from a suitable fractionation step or steps, forexample, as described in said copending case.

The vapors and gases under superatmospheric pressure and at lowtemperature are fractionated in the tower 202, suitable redux andheating means being provided for the tower. The fraction passingoverhead as a. vapor or gas through line 206 contains hydrogen, methane,ethane'and about 40% by weight of ethylene. The fraction collecting ontrap-out tray 208 and withdrawn through line 2|0 comprises an ethylenefraction and contains about 90% ethylene. The fraction withdrawn fromtrap-out tray 2|2 by means of line 2|4 comprises a Ca cut and containsabout '7 0% by weight of propylene.' The 90% ethylene is by weight.

The fraction collecting on trap-out tray 2|6 and withdrawn through line2|8 lcomprises a. C4 cut containing butadiene and butylenes. The liquidhydrocarbons collecting in the bottom of the fractionating tower 202comprise a light aromatic fraction containing gasoline constituents.This aromatic fraction is withdrawn from the bottom of the tower throughlines 220 and 222 and after combining with the partially cooled aromaticfraction withdrawn from the fractionation tower |14 is further cooled inthe cooler- |85. If desired, the light aromatic fraction may bevvzihdrawn as a separate fraction through line The vaporizing furnaceshown in Figure 2 will now be described. The furnace 230 comprises aradiant heating section 232 and a convection heating section 234. Aplurality of pairs of top burners 236 is provided, these burnersextending adjacent the roof 238 of the radiant heating section forburning fuel in the upper portion of the radiant section. Burners 240are provided in the ends of the radiant heating section for supplyingadditional heat to the radiant section. Single rows of wall tubes 242and 244l are provided in the radiant section adjacent the side wallsthereof.

A preheating section 246 comprising a bundle of tubes is provided in thelower portion of the convection heating section 234 for preheating thefeed oil which is to be Vaporized. The oil to be heated is passedthrough line 248 and then through the bundle of tubes 246 forpreheating.

the hydrocarbon oil. The preheated hydrocarbon oil 1s then subdividedinto two streams,.one stream passing through line 252 and through theone row of wall tubes 242 and the other stream passing through line 254and through the other row of wall tubes 244. In this way two streams ofthe oil are separately heated by radiant heat in the radiant section.

Steam superheated to a relatively high temperature is introduced intothe latter portion of each row of tubes 242 and 24,4. Steam passingthrough line 256 is introduced into an intermediate tube 258 of the row242 of heater tubes. Another stream of superheated steam` is passedthrough line 260 into an intermediate tube 262 of the second row of.heater tubes 244 in the radiant heating section. The separately heatedstreams of oil and steam mixtures are then combined and passed throughline 264 which in Fig aseacos a 5 cooler portion of the convectionheating section 234 for heating a natural gas to an elevatedtemperature. This heated natural gas may be used in a gas fractionationsystem wherel dehydrators are The` fractionating tower |14 is maintainedunder pressure of about 1 85 pounds per square inch and the vapors passoverhead through" line Ill at a temperature oi' about 150 F. to 200,used for removing moisture from the gaseous Preferably about'.163 F.The aromatic gasoline mixture before passing through the low temperaturegas fractionation system. The heated natural gas is used for reactvatingthe dehydrators by removing moisture therefrom.

This invention is `especially adapted for thermally cracking relativelyheavy hydrocarbons 4to produce relatively large amounts of unsaturatedlower boiling hydrocarbons such as ethylene,`

propylene` and butadiene together with aromatic gasoline constituents.The butadiene fraction contains mostly 1, 3 butadiene. One example of,

fraction withdrawn from the bottom of fractionatins tower i'll containssubstantial amounts of benzene, toluene, xylenes and higher aromaticfractions. 'I'his `aromatic fraction corresponds to v about .27.3%weight conversion .of the the vaporized oilbeing fed through line 4I tothe zone 55. 'I he total aromatic fraction is about 28.4% by weight onthe gas oil cracked. Due to the aro, matic constituents, the aromaticgasoline has a l5 high octane number. The process herein disclosed.provides amethod whereby at least 25% by volume of aromatichydrocarbons are produced simultaneously `wtih about 10% by weight ofethylene on the feed of hydrocarbon vapors to conversion zone 55.

i The vapors fractionated in the fractionating system 202 comprise amethane-ethylene cut which is` taken overhead through line 200. Thisfraction is a dilute ethylene fraction and may be Daraflilnic` Virgingas oil of the East Texas type utilized as such or may befurtherfractionated is used as the feed oil. One type of such an oil is a gasoilhaving a gravity of 32.3 A. P. I., an initial of 332 F., 50% off atabout-680 F. and a final boiling point of about 884 F.

' The gas oil is passed through the vaporizing coil I 8 and is heated toa temperature of about 8002 F. to 900' F., Preferably about 820 F. Su-

perheated steam at about 800 to 900 F., prefer-A ably about 820 F. isintroducedinto the latter passes of the vaporizing coil I8 through line2l. The steam introduced at this point is equivalent to about 8.5% byweight of the gas oil vapor leaving tower l2. An equal quantity of steamis introduced near the bottom of tower 42 through line |02.

tower I2.

The vapors containing steam passing overhead from the fractionatingtower 42 are at a temperature of about 775 F. to 850 F., preferablyabout 800 F. and these vapors and steam are passed through theconversionzone wherein they are heated to a temperature of about 1200 F. to 1300F., Vpreferably about 1260 F. lDuring conversion, the pressure ismaintained relatively low and the pressure at the inlet of the coil 55is about pounds per square inch and at the outlet of the coil 55 isabout 15 pounds per square inch. The vapors and steam remain in the con.version zone 55 for about 5.60 seconds. This time may be varied with thetemperature, lower temperatures requiring longer times of reaction.

The products of conversion leaving the con# version zone 55 are mixedwith a sufilcient quantity of cycle gas oil introduced as quench throughline 58 to reduce the temperature of the products of conversion to about500 F. to 700 F., preferably about 600 F.

The vapors leaving the top oi the fractionator 52 are at a temperatureof about 220 F. to 260 F., preferably about 230 F. and after cooling inthe cooler H0, they are at a temperature `of about F. so thatsubstantial quantities of water are condensed in the condenser H0. Thefractionator 82 is maintained under about '7 pounds per square inch. Theseparated vapors and liquids are then passed through the compressors anddrums and the pressure in the .accumulating drum |54 is about 175 poundsper square inch and the temperature is about F.

This makes a total of about 17% of 40 steam by weightv on the gas oilvapors leaving- A to separate ethylene, if desired. The second fractionwithdrawn from trap-out tray 208 comprises a concentrated ethylenefraction. The total ethylene yield corresponds to about 10% by weight30..k on the oil passing to the conversion zone 55, 'I'he vpropyleneyield is about 10% by weighton the oil passing to the conversion zone55. For example, if about 40,000 poundsof oil are passed through zone55per` hour, about 4,000 pounds of ethylene 35 will be produced perhour. When recycle cracking is used, about 15% by weight ethylene andabout 15% by weight of propylene on the feed of hydrocarbons to theconversion zone 55 will be obtained.

The propylene fraction withdrawn through line 2M forms a suitablefraction for treatment in a catalytic polymerization process to producepolymerized gasoline or as a basic material for the' manufacture ofvarious chemicals. The butylene 45 fraction withdrawn from trap-out tray2|5 is preferably treated to separate butadiene there-l from, thebutadiene forming about 20% to 30% of the butylene or C4 fraction, byweight.

When cracking under the preferred conditions given in the example above,the following products are obtained given in weight per cent on the gasoil cracked: i d

By varying the conditions in the above example the yield of ethylene maybe raised to about 12% by weight, the yield of propylene may be raisedto 70. about 12% by weight and the yield of the .butadiene fraction(04H0 may be raised to about 2.5% vby weight. VThe butadiene fractioncontains mostly 1,3 butadiene.

While one example has been given, it is to be 75 understoodthat thisexample is by way of illusa tration only and that the conditions, feedstocks, proportions, etc. may-be varied without departing from thespirit of thisinvention.

I claim: l

l. A method for cracking relatively heavy hydrocarbon liquids to producelower boiling hydrocarbons including olefins and aromatic gasolineconstituents which comprises preheating a feed stock comprising higherboiling hydrocarbons and then passing it through a vaporizing coil,preheating water and then further heating the Water toproducesuperheated steam, introducing a portion ot the superheated steam intothe latter portion of said vaporizing coil for admi'iture withthevhydrocarbons therein, passing the heated and vaporized hydrocarbonsand steam to a separating lzone to separate unvaporized constituentsfrom vapors and steam, introducing another pors, tion of the superheatedsteam into the bottom of vfromvapors, fractionating the vapors from saidpassing at least a. portion of the heavy condensate Cil oil in indirectheat exchange with the Water to preheat the water, then passing theheavy condensate oil in indirect heat exchange with the feed stock topreheat the feed stock 4and cool the heavy condensate oil, then using'atleast a. part of the cooled heavy condensate oil without othersubstantial cooling as quench in the quenching step, introducing atleast another portion of the cooled heavy condensate oil without othersubstantial cooling into the top portion of the second separating zoneas reflux to remove heavier hydrocarbons from the vapors, furthertreating the separated lighter hydrocarbons to separate agasoline-containing liquid from vapors and gases and separating ahydrocarbon fraction from said vapors and gases which contains a largeproportion of ethylene.

2'. A method as defined in claim l in which another portion of thecooled heavy condensate oil is used as reflux during fractionation ofthe vapors leaving the second separating zone to remove higher boilinghydrocarbons from the vapors.

BROOK I. SMITH.

